This application claims priority from the following Australian provisional patent applications, the full contents of which are hereby incorporated by cross-reference.
1. Field of the Invention
The present invention relates to coatings and in particular coatings for building products and laminated building products, and composite products incorporating the same.
2. Description of the Related Art
Any discussion of the prior art throughout the specification should in no way be considered as an admission that such prior art is widely known or forms part of common general knowledge in the field.
There are a huge variety of mechanisms for applying coatings to building products such as building boards.
The coatings can be divided into two main groups namely finishing coatings, which are intended primarily for aesthetic purposes, and functional coatings which provide some additional structural or other property/attribute to the resultant product.
The application technique depends to a large extent on the properties of the coating composition and base layer or product to be coated. Manual application and spraying etc are most popular but they restrict the types of coating to be applied and indeed the building product to be coated. For example, when using a spray technique, one must ensure the coating composition is of sufficient flowability to pass through the spray nozzle but at the same time, the base material to be coated must be sufficiently rigid to withstand the impact of the spray coating.
For certain building products, such as internal wall systems, a smooth surface finish is vital. Gypsum or plaster board is used almost exclusively as an internal wall board due to its excellent surface finish.
The use of fibre reinforced cement building board for instance as an internal wall board has significant advantages including cost and structural integrity as compared with gypsum board. However, some techniques for production of fibre reinforced cement sheets do not provide a gypsum like surface finish. In response to public demand, builders require an internal wall board with a near perfect surface finish. Even minute irregularities which arise from production of fibre reinforced cement sheets can be sufficient to reject the product. Sanding the surface of the FRC sheet has been used to improve its surface finish but in some instances such sanding can xe2x80x98featherxe2x80x99 or leave exposed the reinforcing fibres thereby exacerbating the problem.
It is an object of the present invention to overcome or ameliorate at least one of the disadvantages of the prior art, or to provide a useful alternative.
In a first aspect, the present invention provides a method for coating a building product comprising providing a coating formulation including a hydraulic binder and a quantity of dewatering agent, producing a slurry of said formulation, applying said slurry to the product to be coated and dewatering said slurry through said product.
In a second aspect, the present invention provides a formulation for use in coating a building product comprising a hydraulic binder and a quantity of dewatering agent sufficient to permit dewatering of a slurry produced from said formulation through the building product.
In a third aspect, the present invention provides a dewaterable slurry for coating a building product, said slurry comprising water, a hydraulic binder and a quantity of dewatering agent sufficient to permit dewatering of said slurry through said building product.
In a fourth aspect, the present invention provides a composite product comprising a base structural layer with a coating thereon, the coating including a hydraulic binder and a quantity of dewatering agent sufficient such that the coating may be dewatered through the base layer.
In a fifth aspect, the present invention provides a method of making and improving a hydraulic binder based coating formulation for coating a building product comprising adding to said binder a quantity of dewatering agent such that after application of a slurry of said formulation to said building product, said slurry can be dewatered through the building product.
In a sixth aspect, the present invention provides a dewatering aid for dewatering a cementitious slurry coating on a product, said dewatering aid comprising a quantity of particulate material sufficient to permit dewatering of the slurry through the product to be coated.